Boron abundances of B stars of the Orion association

The boron abundance of four B-type stars from the Orion association has been determined from Goddard High Resolution Spectrograph (GHRS)/Hubble Space Telescope (HST) spectra covering the B II 1362 Angstrom resonance line. After correction for large non-LTE effects, the mean boron abundance is similar to the meteoritic abundance, but a factor of 4 (0.6 dex) greater than published abundances of boron in interstellar gas. This difference in boron abundance between young stars and gas is unexplained. The Orion stars were selected by their oxygen abundances: two are enriched in oxygen by about 60% relative to the others. Analysis of the GHRS spectra shows that the O-rich stars are deficient in boron by about 250% (0.4 dex) relative to the O-poor stars. Then, if the differences in oxygen abundance reflect differing levels of contamination of the natal clouds with (O-rich) ejecta of local Type II supernovae, the ejecta were not enriched in boron synthesized by the v-process.